This invention relates to a method for dyeing the jute backing of discernible nylon carpet without discrenible staining of the nylon face fibers. More particularly, it relates to the use of particular imidazolines as a reserving agent for the face fibers of a multilevel nylon carpet having a jute backing to prevent or minimize their staining when the backing is dyed with cationic (basic) type dyestuffs.
Multi-colored nylon carpets are preferrably made by dyeing carpet having two or more different multilevel nylon face fibers with different colored anionic and cationic dyestuffs. Multilevel (or "differential-dyeable") nylon fibers are fibers made from polyamides having only either anionic or cationic groups (sometimes in different quantities so as to be dyeable to different shades) so as to be selectively dyeable with only dyestuffs of a particular class. Typically, the face fibers are dyed before the jute backing, which is after-dyed in a second operation with special cationic dyes at low temperatures, e.g. usually at 100.degree.F. or less.
However, this procedure has had limited application because of the propensity of many jute dyes to cause an unacceptable degree of staining of the carpet face fibers. Recently it has been found that certain quaternary cationic surfactants would function as reserving agents for the multilevel nylon face fibers and yet permit satisfactory exhaust of the jute dye. A description of these cationic surfactants, the problems associated with producing jute-backed multi-colored nylon carpeting, and previous efforts to solve these problems, is provided in U.S. Pat. No. 3,758,269 and the article "Nylon Carpet" by Frederich Bartsch appearing in the September 1973 issue of American Dyestuff Reporter.
While these quaternary cationic surfactants are allegedly satisfactory, there still exists a need for alternative antistaining agents in view of the multitude of different nylon fibers and jute dyes employed in the carpet industry, and, further, considering the always present desire of the industry for materials of lower cost and/or toxicity.